The multidimensional nutritional niche of fungus-cultivar provisioning in free-ranging colonies of a neotropical leafcutter ant

Foraging trails of leafcutter colonies are iconic scenes in the
Neotropics, with ants collecting freshly-cut plant fragments to provision
a fungal food crop. We hypothesized that the fungus-cultivar’s
requirements for macronutrients and minerals govern the foraging niche
breadth of Atta colombica leafcutter ants. Analyses of plant fragments
carried by foragers showed how nutrients from fruits, flowers, and leaves
combine to maximize cultivar performance. While the most commonly foraged
leaves delivered excess protein relative to the cultivar’s needs, in vitro
experiments showed that the minerals P, Al, and Fe may expand the
leafcutter foraging niche by enhancing the cultivar’s tolerance to
protein-biased substrates. A suite of other minerals reduces cultivar
performance in ways that may render plant fragments with optimal
macronutrient blends unsuitable for provisioning. Our approach highlights
how the nutritional challenges of provisioning a mutualist can govern the
multidimensional realized niche available to a generalist insect
herbivore.